What should I check first if I see symptoms of 100MB gigabit internet?

First, proceed with the ‘Check LAN cable and router port’ step. For wired connections, cable/port problems must be ruled out first. We recommend that you avoid changing multiple settings at once and check to see if your symptoms change after each step.

How do I check for the possible cause ‘faulty 4-pair cable’?

If there is no change in the first step, compare in order through ‘Testing the same line on another device.’ If symptoms disappear immediately after certain actions or the conditions for their occurrence change, this can be an important clue in narrowing down the cause.

I have Gigabit Internet, but the Ethernet link only supports 100Mbps: When do I need a professional inspection?

Even if you follow the above solution steps in order, if the Giga Internet 100MB symptoms recur or hardware abnormal signals such as a burning smell, abnormal noise, overheating, or component recognition failure appear together, we recommend backing up important data and having a professional inspection.

PC FIX

Computer Troubleshooting Guide

Internet

Gigabit Ethernet link runs at only 100Mbps

If “Giga Internet 100MB” repeats, it is better to narrow down the scope starting from a defective 4-pair cable and port negotiation settings rather than changing several settings at once. Check the LAN cable/router port and IP allocation status first, and then perform driver and network initialization later.

Solving Order
We've organized the methods starting with the simplest and least expensive ones. Please check the solutions one by one, starting from the top.

Do you have these symptoms?

Giga Internet 100MB
Link speed 100Mbps
Not 1Gbps

main causes

Cable 4 pair defective
Port negotiation settings
Router/NIC limitations

How to solve

Please check them in order from the top. If the issue is resolved, you do not need to proceed to the next step.

Check LAN cable and router port

For wired connections, cable/port problems must be ruled out first.

Difficulty Easy time 5 minutes cost 0 won

1Reconnect the LAN cable on both the PC and the router.
2Connect to another LAN port on the router.
3If possible, replace with another good Cat5e or higher cable.

confirmation point

After these steps, check if the “Giga Internet 100MB” symptom decreases or disappears. If there is no change, check the possibility of a defective 4-pair cable in the next step.

Test the same line on another device

Separate PC NIC problems from router/ISP problems.

Difficulty Easy time 10 minutes cost 0 won

1If you have another PC or USB-Ethernet adapter, test it with the same cable.
2Also check if Wi-Fi is working but the wired connection is not working.

Obtain a new IP address and reset DNS cache

If the DHCP/TCP/IP status is messed up, you can recover the connection.

Difficulty Moderate time 10-15 minutes cost 0 won

1Open an administrator terminal.
2Run ipconfig /renew after ipconfig /release.
3Run ipconfig /flushdns and netsh winsock reset and reboot.

Update or reinstall Ethernet drivers

Outdated or corrupted Ethernet drivers can cause the symptom.

Difficulty Moderate time 10~30 minutes cost 0 won

1Check the device in Device Manager.
2Check your PC or component manufacturer's site for Ethernet drivers for your current model.
3If the problem started immediately after an update, consider rolling back to the previous stable version.
4After installing the driver, restart your PC.

Use network reset as the final step

Reconfigure adapter and network settings to default.

Difficulty Moderate time 15-30 minutes cost 0 won

1Open Settings → Network & Internet → Advanced network settings → Reset network.
2Notice that your VPN/virtual switch settings may disappear.
3After resetting, reboot your PC.

Frequently Asked Questions

We've put together a list of things we frequently check regarding this issue.

Related issues

If the symptoms do not match exactly, please check the issue below.

Internet

No internet connection despite connecting an Ethernet cable

Among Internet problems, the “wired Internet not working” symptom may be related to cable/router ports or network adapter drivers. Check the LAN cable/router port and IP allocation status first, and then perform driver and network initialization later.

View solutions →

Internet

Problem with unidentified network appearing on Ethernet

If “unidentified network” repeats, it is better to narrow it down to DHCP failure or IP setting conflict rather than changing several settings at once. Check the LAN cable/router port and IP allocation status first, and then perform driver and network initialization later.

View solutions →

Internet

Computer suddenly unable to connect to internet

When troubleshooting a computer that suddenly fails to connect to the Internet, it is important to rule out the causes one at a time. Based on the “No Internet” symptom, check the router/modem or ISP problem and the network adapter/IP/DNS settings, then proceed to the next step. Compare with other devices and wired connections to narrow down where the problem occurs: PC, router, or ISP.

View solutions →

Internet

Internet not working after Windows update

If “No internet after update” repeats, it is better to narrow the scope to updated network drivers and changes to TCP/IP settings rather than changing several settings at once. Compare with other devices and wired connections to narrow down where the problem occurs: PC, router, or ISP.

View solutions →

Look for other symptoms too

If you enter the symptoms you are currently seeing in the PC FIX search box, we will find the related problem.

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